Group by…..Having Clause

  Select column1, column2, column3, aggregate_function(expression )

           From TableName Where (condition)

           Group By Column1, column2, column3

For Example, suppose we have a table named EmpInfo which contains the information about the Id of the employee and the Id of the project and it contains the following data

————————–

1                          1

2                          2

3                          2

4                          2

5                          3

Now suppose we want to know about the number of employee belonging to each project then we can use the group by clause as given below:-

select Projectid , count(employeeid) as NumberOfEmployee  from  EmpInfo  Group by ProjectId

ProjectId     NumberOfEmployee

1                    1

2                    3

3                    1

Having Clause :- Having clause is used in conjunction with the group clause by imposing a condition on the group by clause to further filter the records return by the group by clause.

       Select column1, column2, column3, aggregate_function(expression )

       From TableName Where (condition)

For example, suppose we want to know which project has more than 2 employee and the total no of their respective employees, we can use the following query

The query will give us the following result:-

In the above example, the Having clause further filter the result return by the Group By clause by imposing a condition that only those projectid will be shown who has more than 2 employee.